This invention relates to technology for maintaining communication quality and communication reliability in a local-area network (LAN). This technology is applicable to frame forwarding installations such as routers and switches that construct a LAN, is highly likely to be applied in the future and is essential in terms of improving the quality and reliability of networks.
More specifically, the present invention relates to a frame forwarding installation in a network such as a LAN and, more particularly, to a frame forwarding installation for sending frames, which require a real-time property and quality/reliability, to plurality of paths, and to a frame forwarding installation for accepting, and transmitting to a destination terminal, only a first arriving frame of identical frames that arrive from a plurality of paths, and discarding frames other than the first arriving frame.
It is required that the quality and reliability of communication in networks be improved. In order to improve the quality of communication in a conventional LAN, frame transmission delay and transmission fluctuation (a variance in transmission delay) are reduced. To achieve this, processing speed is raised by using hardware to implement routing processing or by executing preferential processing in regard to frames having priority.
Achieving an improvement in reliability is carried out by adopting so-called redundancy or by adopting a so-called hot-standby method, in which the LAN device itself is provided with redundancy to establish active and standby channels so that the standby channel will be switched to automatically if the active channel fails.
Meanwhile, it has been decided that there will be one path from a transmission source to a destination in a LAN. In order to generate the path automatically, the optimum path is calculated using a routing protocol referred to as RIP (Routing Information Protocol) or OSPF (Open Shortest Path First). If a failure occurs, the path can be changed dynamically. There are also occasions where static routing is performed to decide a static path using an address table. In either case, however, there is only one end-to-end path in a LAN at one time.
Thus, in the prior art, an improvement in reliability and quality is attempted on a single path. As a consequence, even if it is attempted to improve quality by improving processing performance at each node in a network or by performing preferential control, frame processing is delayed if a point along the path develops a very high load, thus making it difficult to maintain communication quality. Further, even if it is attempted to improve reliability by adopting redundancy in devices and modules, this does not redress faults in the transmission line, for example, and it is therefore not possible to assure perfect reliability.